title: A normalized PID controller in networked control systems with varying time delays.
abstract: It requires not only simplicity and flexibility but also high specified stability and robustness of system to design a PI/PID controller in such complicated networked control systems (NCSs) with delays. By gain and phase margins approach, this paper proposes a novel normalized PI/PID controller for NCSs based on analyzing the stability and robustness of system under the effect of network-induced delays. Specifically, We take into account the total measured network delays to formulate the gain and phase margins of the closed-loop system in the form of a set of equations. With pre-specified values of gain and phase margins, this set of equations is then solved for calculating the closed forms of control parameters which enable us to propose the normalized PI/PID controller simultaneously satisfying the following two requirements: (1) simplicity without re-solving the optimization problem for a new process, (2) high flexibility to cope with large scale of random delays and deal with many different processes in different conditions of network. Furthermore, in our method, the upper bound of random delay can be estimated to indicate the operating domain of proposed PI/PID controller. Finally, simulation results are shown to demonstrate the advantages of our proposed controller in many situations of network-induced delays.
authors.affiliation: College of Automation, Huazhong University of Science and Technology, Wuhan 430074, PR China.
authors.forename: Hoang-Dung
authors.initials: HD
authors.lastname: Tran
authors.forename: Zhi-Hong
authors.initials: ZH
authors.lastname: Guan
authors.forename: Xuan-Kien
authors.initials: XK
authors.lastname: Dang
authors.forename: Xin-Ming
authors.initials: XM
authors.lastname: Cheng
authors.forename: Fu-Shun
authors.initials: FS
authors.lastname: Yuan
keywords: Gain and phase margins; Networked control systems; PID tuning; Time delays